This application pertains to the art of indicators and, more particularly, to indicators for indicating overtravel of a piston in a cylinder. The invention is particularly applicable for use in a pressure converter for converting pneumatic pressure to hydraulic pressure, and will be particularly described with reference thereto. However, it will be appreciated that the invention has broader aspects and may be used in other devices having pistons which may overtravel.
This application relates generally to a piston overtravel indicator of the type disclosed in U.S. Pat. No. 3,997,887 issued Dec. 14, 1976, to Poynter. In the arrangement of the Poynter patent, an elongated indicator rod extends through a hole in an end wall of a pneumatic cylinder. Overtravel of the pneumatic piston beyond its normal working positions causes same to engage the inner end of the indicator rod for pushing same outwardly. A switch cooperating with the indicator rod is closed by axial outward movement of the indicator rod for energizing an audible or visual signal.
In the arrangement of the Poynter patent, the indicator rod is held against complete outward displacement from the cylinder by a snap ring received in a circumferential groove adjacent the inner end of the indicator rod. The snap ring extends radially outwardly of the indicator rod a distance greater than the diameter of the hole through which the indicator rod slides. The snap ring will engage the inner surface of a cylinder end wall for preventing complete outward displacement of the indicator rod. This arrangement makes it impossible to completely remove the indicator rod without completely disassembling the entire pneumatic cylinder. The arrangement of Poynter with the snap ring also requires assembly of the indicator rod and snap ring prior to assembly of the other cylinder parts because the inner end portion of the indicator rod is not accessible once the cylinder is assembled. The use of a snap ring requires additional assembly and it would be desirable to simplify the arrangement for preventing complete outward displacement of the indicator rod.
It is a principal object of the present invention to provide an improved indicator for indicating overtravel of a piston.
It is also an object of the invention to provide an improved integral stop means for preventing complete outward displacement of an indicator rod.
It is a further object of the invention to provide an improved indicator rod having a stop for preventing complete outward displacement thereof, while permitting assembly of the indicator rod subsequent to assembly of the complete cylinder.
It is an additional object of the invention to provide an improved indicator rod which may be removed and replaced without disassembly of the entire cylinder on which it is mounted.